1. Field of the Invention
This invention relates to a communications system and, more particularly, to a communications system which accommodates a plurality of different types of lines.
2. Description of the Prior Art
Communications systems such as facsimile machines and telephones which have a so-called auto-repeat function (automatic redial function) are known in the art. With an auto-repeat function, the system repeatedly calls another party automatically at prescribed time intervals if a connection with the party cannot be established because the party is currently communicating, or for some other reason.
The auto-repeat function of a Key Telephone System is adapted to acquire, at redialing, the same line dialed the preceding time, or to perform a search in ascending or descending order in accordance with the physical accommodation position of the line in order to acquire a line which is idle.
Further, in a Key Telephone System, by way of example, conventionally an idle outside line is acquired by pressing an outside-line button on an extension telephone, or by pressing a button having a special number, such as 0, when the extension is in a state in which it is capable of initiating an intercom call.
In another arrangement, it is also possible to acquire an outside line, and to establish a state in which a transmission can be made with the outside line, by picking up a handset or by pressing a special button (e.g., a speaker button) on an extension telephone without lifting the handset.
However, in the conventional communications system having the auto-repeat function, at redialing a line is acquired without relation to the data dialed in at the time of the initial transmission. This leads to the following drawbacks:
(1) Ordinarily, the user dials in accordance with the acquired line and the party called. For example, the user dials "789-1111" when a call is placed through a public telephone network; "0-789-1111" when the call is placed to the same party through a PBX line; and a two- to four-digit number, for example, upon acquiring a PBX line, when another extension connected to the PBX line is dialed. Consequently, when a line of a different type is acquired at the time of a retransmission and the previous dial data is transmitted as is, erroneous dialing is the result.
(2) In a case where the line acquired is physically identical with that previously, this line, even if it is unused, is always the same as that reserved by the auto-repeat function, and therefore the line cannot be utilized by other extensions.
Further, in a case where the above-described conventional telephone system accommodates a plurality of mixed outside lines such as an analog PBX extension, a digital public switched telephone network and an international telephone line, the following problems arise:
(1) In a case where an outside-line button provided on an extension telephone is pressed to acquire an outside line, it is necessary to memorize to which button the desired line has been assigned. This is very troublesome.
(2) In a case where an idle outside line is acquired by dialing 0 or a special number or merely by picking up the headset, the user cannot determine the kind of outside line that has been acquired.
(3) When the user dials the other party without knowing the type of outside line in case (2) above, there is a very high probability that erroneous dialing will take place.
(4) Even an outside line of a type not desired for selection may be acquired if this line is idle.
(5) Since an idle outside line of a type desired for selection can be acquired by another extension as well, a busy signal or the like can be encountered so that the line cannot be used.